'\"! eqn | mmdoc
'\"macro stdmacro
.ds Vn Version 1.2
.ds Dt 6 March 1997
.ds Re Release 1.2.0
.ds Dp Feb 16 02:56
.ds Dm  Feb 10 17:2
.ds Xs 60987 10 xgetconfig.gl
.TH GLXGETCONFIG 3
.SH NAME
glXGetConfig
\- return information about GLX visuals

.SH C SPECIFICATION
int \f3glXGetConfig\fP(
Display \fI*dpy\fP,
.nf
.ta \w'\f3int \fPglXGetConfig( 'u
	XVisualInfo \fI*vis\fP,
	int \fIattrib\fP,
	int \fI*value\fP )
.fi

.EQ
delim $$
.EN
.SH PARAMETERS
.TP \w'\fIattrib\fP\ \ 'u 
\f2dpy\fP
Specifies the connection to the X server.
.TP
\f2vis\fP
Specifies the visual to be queried.
It is a pointer to an \f3XVisualInfo\fP structure,
not a visual ID or a pointer to a \f3Visual\fP.
.TP
\f2attrib\fP
Specifies the visual attribute to be returned.
.TP
\f2value\fP
Returns the requested value.
.SH DESCRIPTION
\f3glXGetConfig\fP sets \f2value\fP to the \f2attrib\fP value of windows or GLX pixmaps
created with respect to \f2vis\fP.
\f3glXGetConfig\fP returns an error code if it fails for any reason.
Otherwise, zero is returned.
.P
\f2attrib\fP is one of the following:
.P
.TP 22
\f3GLX_USE_GL\fP
\f3True\fP if OpenGL rendering is supported by this visual,
\f3False\fP otherwise.
.TP
\f3GLX_BUFFER_SIZE\fP
Number of bits per color buffer.
For RGBA visuals, \f3GLX_BUFFER_SIZE\fP is the sum of
\f3GLX_RED_SIZE\fP,
\f3GLX_GREEN_SIZE\fP,
\f3GLX_BLUE_SIZE\fP, and
\f3GLX_ALPHA_SIZE\fP.
For color index visuals, \f3GLX_BUFFER_SIZE\fP is the size of the
color indexes.
.TP
\f3GLX_LEVEL\fP
Frame buffer level of the visual.
Level zero is the default frame buffer.
Positive levels correspond to frame buffers that overlay the default buffer,
and negative levels correspond to frame buffers that underlay the default
buffer.
.TP
\f3GLX_RGBA\fP
\f3True\fP if color buffers store red, green, blue, and alpha values.
\f3False\fP if they store color indexes.
.TP
\f3GLX_DOUBLEBUFFER\fP
\f3True\fP if color buffers exist in front/back pairs that can be swapped,
\f3False\fP otherwise.
.TP
\f3GLX_STEREO\fP
\f3True\fP if color buffers exist in left/right pairs,
\f3False\fP otherwise.
.TP
\f3GLX_AUX_BUFFERS\fP
Number of auxiliary color buffers that are available.
Zero indicates that no auxiliary color buffers exist.
.TP
\f3GLX_RED_SIZE\fP
Number of bits of red stored in each color buffer.
Undefined if \f3GLX_RGBA\fP is \f3False\fP.
.TP
\f3GLX_GREEN_SIZE\fP
Number of bits of green stored in each color buffer.
Undefined if \f3GLX_RGBA\fP is \f3False\fP.
.TP
\f3GLX_BLUE_SIZE\fP
Number of bits of blue stored in each color buffer.
Undefined if \f3GLX_RGBA\fP is \f3False\fP.
.TP
\f3GLX_ALPHA_SIZE\fP
Number of bits of alpha stored in each color buffer.
Undefined if \f3GLX_RGBA\fP is \f3False\fP.
.TP
\f3GLX_DEPTH_SIZE\fP
Number of bits in the depth buffer.
.TP
\f3GLX_STENCIL_SIZE\fP
Number of bits in the stencil buffer.
.TP
\f3GLX_ACCUM_RED_SIZE\fP
Number of bits of red stored in the accumulation buffer.
.TP
\f3GLX_ACCUM_GREEN_SIZE\fP
Number of bits of green stored in the accumulation buffer.
.TP
\f3GLX_ACCUM_BLUE_SIZE\fP
Number of bits of blue stored in the accumulation buffer.
.TP
\f3GLX_ACCUM_ALPHA_SIZE\fP
Number of bits of alpha stored in the accumulation buffer.
.TE
.P
The X protocol allows a single visual ID to be instantiated with
different numbers of bits per pixel.
Windows or GLX pixmaps that will be rendered with OpenGL, however,
must be instantiated with a color buffer depth of \f3GLX_BUFFER_SIZE\fP.
.P
Although a GLX implementation can export many visuals that support GL
rendering,
it must support 
at least one RGBA visual. This visual must have at 
least one color buffer,
a stencil buffer of at least 1 bit,
a depth buffer of at least 12 bits,
and an accumulation buffer.
Alpha bitplanes are optional in this visual.
However,
its color buffer size must be as great as that of the
deepest \f3TrueColor\fP, \f3DirectColor\fP,
\f3PseudoColor\fP, or \f3StaticColor\fP visual supported on level zero,
and it must itself be made available on level zero.
.P
In addition, if the X server exports a \f3PseudoColor\fP 
or \f3StaticColor\fP visual on framebuffer level 0, a color index 
visual is also required on that level.
It must have  
at least one color buffer,
a stencil buffer of at least 1 bit,
and a depth buffer of at least 12 bits.
This visual must 
have as many 
color bitplanes as the deepest
\f3PseudoColor\fP or \f3StaticColor\fP visual supported on level 0.
.P
Applications are best written to select the visual that most closely
meets their requirements.
Creating windows or GLX pixmaps with unnecessary buffers can result in
reduced rendering performance as well as poor resource allocation.
.SH NOTES
\f3XVisualInfo\fP is defined in \f2Xutil.h.\fP
It is a structure that includes \f2visual\fP, \f2visualID\fP, \f2screen\fP, and
\f2depth\fP elements.
.SH ERRORS
\f3GLX_NO_EXTENSION\fP is returned if \f2dpy\fP does not support the GLX
extension.
.P
\f3GLX_BAD_SCREEN\fP is returned if the screen of \f2vis\fP does not correspond
to a screen.
.P
\f3GLX_BAD_ATTRIBUTE\fP is returned if \f2attrib\fP is not a valid GLX attribute.
.P
\f3GLX_BAD_VISUAL\fP is returned if \f2vis\fP doesn't support GLX and an
attribute other than \f3GLX_USE_GL\fP is requested.
.SH SEE ALSO
\f3glXChooseVisual\fP,
\f3glXCreateContext\fP

